Multipath mitigation circuit for home network

ABSTRACT

A filter circuit is provided having multipath interference mitigation. The filter includes a signal path extending from an input to an output. The signal path includes a conductive path and a ground. A pass band filter is disposed along the signal path between the input and the output. The pass band filter passes a first frequency spectrum in a provider bandwidth, and attenuates a second frequency spectrum in a home network bandwidth. The filter circuit further includes a multipath interference mitigation leg operatively branched from the signal path. The multipath interference mitigation leg increases a return loss of the home network bandwidth. A frequency response of the filter circuit is characterized by an insertion loss characteristic between the input and the output being less than 3 dB in the provider bandwidth, and more than 20 dB in the home network bandwidth. The frequency response is further characterized by a return loss characteristic at the output being more than 10 dB in the provider bandwidth and home network bandwidth.

FIELD OF THE INVENTION

The present invention relates generally to an electronic filter assemblyfor use in the cable television (CATV) industry, and more specificallyto a circuit assembly that mitigates home data network signals fromreflecting within a user's network.

BACKGROUND OF THE INVENTION

In many data distribution networks, electrical signals conveyinginformation propagate along transmission lines across distances andthrough splitting devices. For example, in a cable television (CATV)network, media content propagates downstream from a head-end facilitytoward media devices located in various facilities such as homes andbusinesses. Along the way, the electrical signals conveying the mediacontent propagate along main trunks, through taps, and along multiplebranches that ultimately distribute the content to drop cables atrespective facilities. The drop cable, which may be a single coaxialcable, typically is connected to a splitting device having two or moreoutlet ports. Distribution cables connected to the outlet ports routethe signals to various rooms, often extending to one or more mediadevices. The network of distribution cables, splitters, and distributionpoints is referred to as a drop system.

A typical data distribution network provides many content selections toa user's media devices within the drop system, such as one or moretelevisions equipped with set top boxes or cable modems. Contentselection propagated on a downstream bandwidth of the CATV system mayinclude broadcast television channels, video on demand services,internet data, home security services, and voice over internet (VOIP)services. The content selections are typically propagated in a discretefrequency range, or channel, that is distinct from the frequency rangesof other content selections. Downstream bandwidth includes frequenciestypically ranging from 50-1,000 megahertz (MHz).

The typical data distribution network is a two-way communication system.The downstream bandwidth carries signals from the head end to the userand an upstream bandwidth carries upstream signals from the user to thehead end. Upstream bandwidth may include data related to video on demandservices, such as video requests and billing authorization; internetuploads, such as photo albums or user account information; securitymonitoring; or other services predicated on signals or data emanatingfrom a subscriber's home. Upstream bandwidth frequencies typically rangefrom 7-49 MHz.

A user data network, or home network, may be coupled to the cabletelevision network via the same coaxial cable delivering the downstreamand upstream bandwidth of the CATV system. Often, the user data networkis a home entertainment network providing multiple streams of highdefinition video and entertainment. Examples of home networkingtechnologies include Ethernet, HomePlug, HPNA, and 802.11n. In anotherexample, the user data network may employ technology standards developedby the Multimedia over Coax Alliance (MoCA). The MoCA standards promotenetworking of personal data utilizing the existing coaxial cable that isalready wired throughout the user premises. MoCA technology provides thebackbone for personal data networks of multiple wired and wirelessproducts including voice, data, security, home heating/cooling, andvideo technologies. In such an arrangement, the cable drop from thecable system operator shares the coaxial line or network connection withMoCA-certified devices such as a broadband router or a set top box. Theoperators use coaxial wiring already existing within the home orbusiness to interconnect the wired and wireless MoCA devices by directlyconnecting them to the coaxial jacks throughout the premises. MoCAtechnology delivers broadband-caliber data rates exceeding 130 Mbps, andsupports as many as sixteen end points.

A MoCA-certified device such as the broadband router interconnects otherMoCA-certified components located within the premises, for exampleadditional set top boxes, routers and gateways, bridges, optical networkterminals, computers, gaming systems, display devices, printers,network-attached storage, and home automation such as furnace settingsand lighting control. The home network allows distribution and sharingof data or entertainment content among the MoCA-connected devices. Forexample, a high definition program recorded on a set top box in theliving room may be played back by a second set top box located in abedroom. And, a high definition movie recorded on a camcorder and storedon a user's personal computer may be accessed and displayed through anyof the set top boxes within the premises. The home network may alsoallow high-definition gaming between rooms.

The home network may utilize an open spectrum bandwidth on the coaxialcable to transmit the personal data content, such as entertainmentcontent. For example, a cable system operator may utilize a bandwidth offrequencies up to 1002 MHz, and a satellite system operator may utilizea bandwidth of frequencies from 1550-2450 MHz. The unused range offrequencies in this example, or open spectrum bandwidth, is 1002-1550MHz. In another example, the open spectrum bandwidth may be higher than2450 MHz. In one particular example, the Multimedia over Coax Alliancespecifies an open spectrum, or home network bandwidth, of 1125-1525 MHz.A home network utilizing the open spectrum bandwidth does not interferewith any of the bandwidth being utilized by the cable television orsatellite services provider.

An exemplary filter designed for use in a MoCA network is installed atthe point of entry to a premises to allow MoCA transmissions topropagate throughout the home network while preventing the them frominterfering with adjacent subscribers in the CATV network. Thus, theMoCA filter passes signals in the provider bandwidth and attenuatessignals in the home network bandwidth. One problem noted with existingMoCA filters attenuating the home network spectrum is multipathinterference. Multipath interference, or distortion, is a phenomenon inthe physics of waves in which a wave from a transmitter travels to areceiver via two or more paths and, under the right conditions, two ormore of the wave components interfere. The interference arises due tothe wave components having travelled a different path defined bydiffraction and the geometric length. The differing speed results in thewave components arriving at the receiver out of phase with each other.Multipath interference is a common cause of “ghosting” in analogtelevision broadcasts, and is exacerbated in a MoCA network because theMoCA standard requires very high transmission energy (e.g., low powerloss in the MoCA bandwidth). This high transmission power results ingreater reflections at the ports of devices.

SUMMARY OF THE INVENTION

A filter circuit is provided having multipath interference mitigation.In one aspect of the invention, the filter includes a signal pathextending from an input to an output. The signal path includes aconductive path and a ground. A pass band filter is disposed along thesignal path between the input and the output. The pass band filterpasses a first frequency spectrum in a provider bandwidth, andattenuates a second frequency spectrum in a home network bandwidth. Thefilter circuit further includes a multipath interference mitigation legoperatively branched from the signal path. The multipath interferencemitigation leg increases a return loss of the home network bandwidth. Afrequency response of the filter circuit is characterized by aninsertion loss characteristic between the input and the output beingless than 3 dB in the provider bandwidth, and more than 20 dB in thehome network bandwidth. The frequency response is further characterizedby a return loss characteristic at the output being more than 10 dB inthe provider bandwidth and home network bandwidth.

In one aspect of the invention, the multipath interference mitigationleg is terminated to ground.

In a further aspect of the invention, the multipath interferencemitigation leg is terminated to ground and includes an absorptivecircuit.

In a further aspect of the invention, the absorptive circuit is aChebyshev filter circuit.

In another aspect of the invention, the multipath interferencemitigation leg is branched in parallel with the pass band filter.

In a further aspect of the invention, the multipath interferencemitigation leg is branched in parallel with the pass band filter andincludes an attenuator portion.

In a further aspect of the invention, the attenuator portion is aTee-type resistive attenuator.

In another aspect of the invention, the frequency response of thecircuit is further characterized by the return loss at the output andthe input being more than 20 dB in the provider bandwidth and homenetwork bandwidth.

BRIEF DESCRIPTION OF THE DRAWINGS

For a further understanding of the invention, reference will be made tothe following detailed description of the invention which is to be readin connection with the accompanying drawing, wherein:

FIG. 1 schematically illustrates a portion of a home network;

FIG. 2 is a chart showing the insertion loss and input/output returnloss for a filter circuit within the home network depicted in FIG. 1;

FIG. 3 is a circuit diagram, in schematic form, of one embodiment of afilter in accordance with the present invention;

FIG. 4 is a chart showing the insertion loss and input/output returnloss for the filter circuit shown in FIG. 3;

FIG. 5 is a circuit diagram, in schematic form, of a second embodimentof a filter in accordance with the present invention; and

FIG. 6 is a chart showing the insertion loss and input/output returnloss for the filter circuit shown in FIG. 5.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, a portion of an exemplary home network includes afilter housing 2 located at the point of entry to a premises. In thedisclosed embodiment, the filter housing 2 is a standard femalef-connector configured to pass a provider bandwidth 4, which may be aCATV system, for example. An exemplary CATV system typically includes adownstream component and an upstream component. The provider bandwidth 4may propagate a downstream bandwidth in the 50-1,000 MHz range, and alsocarry an upstream bandwidth in the 7-49 MHz range.

The provider bandwidth 4 passes through a MoCA-enabled splitter 6 havingan input port 8 and two distribution ports 10 a, 10 b respectively. Inone example, distribution port 10 a is coupled via coaxial cable to aMoCA-enabled device 12 such as a wireless router. Distribution port 10 bis coupled to a second MoCA-enabled splitter 14. The second splitter 14likewise includes an input port 16, a second distribution port 18connected to a second MoCA-enabled second device 20, such as a set topbox, and a third distribution port 22 connected to a third MoCA-enabledthird device 24, such as another set top box.

The second splitter 14 is adapted to freely transmit data on a homenetwork bandwidth 26 from any port to any other port. For example, dataon the home network bandwidth 26 may be transmitted from the seconddistribution port 18 to the third distribution port 22. In anotherexample, data may be transmitted in an upstream direction from the firstset top box 20 to the second distribution port 18 and through the secondinput port 16, through the distribution port 10 b, then in a downstreamdirection through distribution port 10 a to the wireless router 12. Thedata may include voice transmission, security, home heating/coolinginstructions, and high definition video technologies, for example. Thehome network bandwidth 26 occupies an open spectrum bandwidth, that is,a frequency range outside the provider bandwidth 4. Referring to theexemplary CATV system above, the home network bandwidth 26 may carrysignals in the 1125-1525 MHz range.

In the disclosed embodiment, the filter housing 2 includes internalfilter circuitry to secure the home network bandwidth 26 from leakingupstream to other houses on the CATV network, thus protecting theprivacy of the home network. One example of the internal filtercircuitry, commonly referred to as a point-of-entry or MoCA filter 28,is described in U.S. patent application Ser. No. 12/501,041 entitled“FILTER CIRCUIT”, which is incorporated herein by reference in itsentirety.

Two important characteristics which determine the performance of thesignals carried by the coaxial device are insertion loss and returnloss. Insertion loss refers to the amount of attenuation the signalreceives as it passes from the input to the output. Return loss refersto a measure of the reflected energy from the transmitted signal. Theloss value is a negative logarithmic number expressed in decibels (dB)however, as used herein, the negative sign is dropped. Thus, a filtercircuit initially having a loss characteristic of 1 dB that is improvedto 20 dB improves (or decreases) the reflected signal level from about80% to about 1%. As a rule of thumb, a 3 dB loss reduces power to onehalf, 10 dB to one tenth, 20 dB to one hundredth, and 30 dB to onethousandth. Therefore, the larger the insertion loss characteristic, theless energy that is lost passing through the circuit. The larger thereturn loss characteristic, the less energy that is reflected. Multipathreturn losses can be generated from splitters, coaxial cable, orpoint-of-entry filters, for example.

Referring to FIG. 2, a frequency response 30 of the exemplary MoCAfilter 28 includes an insertion loss 32 between the connector input andthe connector output. The insertion loss 32 trace can be interpreted tomean that signals in the provider bandwidth 4 (5 MHz-1002 MHZ) arepermitted to pass through the connector, while the signals in the homenetwork bandwidth 26 (1125 MHz-1525 MHz) are attenuated or blocked. Thefrequency response 30 further includes an input return loss 34 orreflection at the connector input port, and an output return loss 36 orreflection at the connector output port. The return losses 34, 36 aregreater than about 20 dB in the pass band, or provider bandwidth 4, butare approximately 1 dB in the stop band, or home network bandwidth 26.

Although the return losses 34, 36 may be adequate in the providerbandwidth 4, very high reflections may be experienced in the homenetwork bandwidth 26. Multipath distortions may be generated from thepoor return loss produced from the filters stop band. Referring now backto FIG. 1, a primary transmission path 38 may be defined by data (suchas high definition programming) propagating on the home networkbandwidth 26 from the first set top box 20 in an upstream direction tothe second distribution port 18 on the MoCA-enabled splitter 14, then ina downstream direction through the third distribution port 22 where itis received by the second set top box 24. In this example, data wouldalso propagate from the second distribution port 18 through the secondinput port 16, through the distribution port 10 b, and would beattenuated at the MoCA filter 28 in the filter housing 2. However,because the output return loss 36 is approximately 1 dB within the homenetwork bandwidth 26, almost all the power is reflected and a secondarytransmission path 40 sets up for the reflected signal. The datapropagating along the secondary transmission path 40 arrives at thereceiver (e.g., set top box 24) out of synch with the data in theprimary transmission path 38, and multipath interference results.

Referring to FIG. 3 of the drawings, wherein like numerals indicate likeelements from FIGS. 1 and 2, one possible topology for an embodiment ofan improved filter circuit 142 is provided that reduces the multipathinterference experienced with prior MoCA filters. The filter circuit 142includes a signal path 144 extending from an input 146 to an output 148.In one example, the input 146 is connected to the input port of thefilter housing, which may be, in turn, in electrical communication witha supplier-side port such as a tap port (not shown). The output 148 maybe adapted to receive signals comprising the provider bandwidth 104, thehome network bandwidth 126, noise, and any other signals present on thecoaxial cable. Conversely, the input 146 may be connected to theuser-side port and the output 148 may be connected to the supplier-sideport.

The signal path 144 includes a conductive path 150, such as the centerconductor in a coaxial cable, to carry the upstream bandwidth, thedownstream bandwidth, and the home network bandwidth. The signal path144 further includes a ground 152, such as the outer sheath of thecoaxial cable that provides a path to ground with various cableconnector devices.

The filter circuit 142 further includes a pass band filter portion 154disposed along the signal path 144 between the input 146 and the output148. The pass band filter portion 154 is configured to pass a firstfrequency spectrum in the provider bandwidth 104 and attenuate a secondfrequency spectrum in the home network bandwidth 126. In one embodiment,the pass band filter portion 154 is a hybrid parallel inductor/capacitor(LC) arrangement in which inductors L4 and L5, along with capacitor C8,increase the isolation of the low pass filter. Resonator or tankelements 156 a-156 c defined by L1/C1, L2/C2, and L3/C3 and capacitiveshunts C4, C5, C6, and C7 collectively form an elliptic filter. Otherfilter designs, such as Butterworth, are equally operable but mayrequire additional components to implement.

The filter circuit 142 further includes a multipath interferencemitigation leg 158 operatively branched to ground from the signal path144. The multipath interference mitigation leg 158 is configured toincrease the return loss in the home network bandwidth. In theembodiment shown in FIG. 3, the multipath interference mitigation leg158 is an absorptive Chebyshev filter circuit that increases the returnloss at the output port of the connector without affecting the frequencyresponse of the remaining circuit. The absorptive circuit includes afirst lumped element comprising capacitors C9 and C10 in series, with aninductor/capacitor (LC) series connection of L6/C13 shunted to ground ata node between C9 and C10. The absorptive circuit further includes asecond lumped element comprising capacitors C10 and C11 in series, withan inductor/capacitor (LC) series connection of L7/C14 shunted to groundat a node between C10 and C11. The absorptive circuit further includes athird lumped element comprising capacitors C11 and C12 in series, withan inductor/capacitor (LC) series connection of L8/C15 shunted to groundat a node between C11 and C12. A termination resistor 160 may beconfigured to match the impedance of the line load so as to preventreflections due to impedance mismatch. In the illustrated example, theline load is 75 ohms, and the termination resistor 160 is likewise 75ohms.

FIG. 4 plots the frequency response 162 of the filter circuit 142 shownin FIG. 3. The insertion loss 132 between the connector input and theconnector output is essentially zero in the provider bandwidth 104, andgreater than 50 dB in the home network bandwidth 126. Thus, the filtercircuit 142 will pass the signals in the provider bandwidth 104 andattenuate the signals in the home network bandwidth 126. The inputreturn loss 134 is essentially unchanged in that the loss of greaterthan 20 dB in the provider bandwidth 104 will reduce reflections fromthe input port of the connector. One noted improvement of the filtercircuit 142 is that the output return loss 136 of the circuit isimproved to greater than 20 dB in both the provider bandwidth 104 andthe home network bandwidth 126. In this manner, reflections at theoutput port are reduced and the strength of the secondary transmissionpath (described in FIG. 1) will be reduced by as much as 99%. Although areturn loss value of more than 20 dB is disclosed, the inventors havediscovered that the return loss at the output may be more than 10 dB inthe provider bandwidth and home network bandwidth, and the filtercircuit of the present invention will still perform adequately.

Referring now to FIG. 5 of the drawings, wherein like numerals indicatelike elements from FIGS. 1 and 2, another topology of an improved filtercircuit 242 is provided that reduces the multipath interferenceexperienced with prior MoCA filters. The filter circuit 242 includes asignal path 244 extending from an input 246 to an output 248. In oneexample, the input 246 is connected to the input port of the coaxialcable connector, which may be, in turn, in electrical communication witha supplier-side port such as a tap port (not shown). The output 248 maybe adapted to receive signals comprising the provider bandwidth 204, thehome network bandwidth 226, noise, and any other signals present on thecoaxial cable. Conversely, the input 246 may be connected to theuser-side port and the output 248 may be connected to the supplier-sideport. Further, the filter circuit 242 may be adapted to filter signalsin both directions (e.g., bi-directional), so the physical location ofthe input 246 and output 248 may be arbitrary.

The signal path 244 includes a conductive path 250, such as the centerconductor in a coaxial cable, to carry the upstream bandwidth, thedownstream bandwidth, and the home network bandwidth. The signal path244 further includes a ground 252, such as the outer sheath of thecoaxial cable that provides a path to ground with various cableconnector devices.

The filter circuit 242 further includes a pass band filter portion 254disposed along the signal path 244 between the input 246 and the output248. The pass band filter portion 254 is configured to pass a firstfrequency spectrum in the provider bandwidth 204 and attenuate a secondfrequency spectrum in the home network bandwidth 226. In this manner,the pass band filter portion 254 is a low pass filter. In oneembodiment, the pass band filter portion 254 is a parallelinductor/capacitor (LC) arrangement in which inductors L1 and L6increase the isolation of the low pass filter. Resonator or tankelements 256 a- 256 d defined by L2/C2, L3/C3, L4/C4, and L5/C5 andcapacitive shunts C1, C6, C7, C8, and C9 collectively form an ellipticfilter. Other filter designs, such as Butterworth, are equally operablebut may require additional components to implement.

The filter circuit 242 further includes a multipath interferencemitigation leg 258 operatively branched to ground from the signal path244. The multipath interference mitigation leg 258 is configured toincrease the return loss in the home network bandwidth. In theembodiment shown in FIG. 5, the multipath interference mitigation leg258 is an attenuator circuit that increases the return loss at theoutput port of the connector without affecting the frequency response ofthe remaining circuit. The attenuator circuit includes a high passfilter portion 264 a, 264 b and an attenuator portion 266. The high passfilter portions 264 a, 264 b are Tee-type circuits in one example, butmay comprise other types. In the disclosed embodiment, the attenuatorportion 266 is a Tee-type resistive attenuator comprising threeresistors R1, R2, and R3. However, other arrangements are contemplated,such as a Pi-attenuator.

FIG. 6 plots the frequency response 268 of the filter circuit 242 shownin FIG. 5. The insertion loss 232 between the connector input and theconnector output is essentially zero in the provider bandwidth 204, andgreater than 40 dB in the home network bandwidth 226. Thus, the filtercircuit 242 will pass the signals in the provider bandwidth 204 andattenuate the signals in the home network bandwidth 226. The inputreturn loss 234 and output return loss 236 are essentially identical dueto the symmetry of the circuit, and comprise a value of greater than 20dB in both the provider bandwidth 204 and the home network bandwidth226. In this manner, reflections at the input port and output port arereduced, and the strength of the secondary transmission path (describedin FIG. 1) will be reduced by as much as 99%.

One advantage provided by the present invention is that home networkmultipath distortions at the filter port connections are minimized oreven eliminated, thereby enhancing signal quality. Prior art filtersdesigned for the MoCA standard, for example, generated significantmultipath distortions from the poor return loss (typically less than 1dB) produced from the filter's stop band.

Many modifications and other embodiments of the inventions set forthherein will come to mind to one skilled in the art to which theseinventions pertain having the benefit of the teachings presented in theforegoing descriptions and the associated drawings. Therefore, it is tobe understood that the inventions are not to be limited to the specificembodiments disclosed and that modifications and other embodiments areintended to be included within the scope of the appended claims. Forexample, although the embodiments disclosed herein comprise analogcircuits, the inventors contemplate digital circuitry could be utilizedwithout departing from the scope of the invention. Further, althoughspecific terms are employed herein, they are used in a generic anddescriptive sense only and not for purposes of limitation.

We claim:
 1. A filter circuit having a frequency response, the filtercircuit comprising: a signal path extending from an input to an output,the signal path comprising a conductive path and a ground; a pass bandfilter portion disposed along the signal path between the input and theoutput, the pass band filter portion configured to pass a firstfrequency spectrum in a provider bandwidth and attenuate a secondfrequency spectrum in a home network bandwidth, wherein the pass bandfilter portion comprises a hybrid parallel inductor/capacitorarrangement having tank elements and isolation inductors; and amultipath interference mitigation leg operatively branched from thesignal path, the multipath interference mitigation leg configured todecrease multipath distortions by improving a return loss characteristicof the home network bandwidth; wherein the frequency response ischaracterized by an insertion loss characteristic between the input andthe output being less than 3 decibels (dB) in the provider bandwidth andmore than 20 dB in the home network bandwidth, the frequency responsefurther characterized by a return loss characteristic at the outputbeing more than 10 dB in the provider bandwidth and more than 20 dB inthe home network bandwidth.
 2. The filter circuit of claim 1, whereinthe frequency response is further characterized by the insertion losscharacteristic being more than 30 dB in the home network bandwidth. 3.The filter circuit of claim 1, wherein the multipath interferencemitigation leg is terminated to the ground.
 4. The filter circuit ofclaim 1, wherein the multipath interference mitigation leg comprises anabsorptive portion.
 5. The filter circuit of claim 4, wherein theabsorptive portion comprises a Chebyshev filter circuit.
 6. The filtercircuit of claim 5, wherein the Chebyshev filter circuit comprises aplurality of Chebyshev filter circuits.
 7. The filter circuit of claim1, wherein the multipath interference mitigation leg further comprises ashunt resistor.
 8. The filter circuit of claim 7, wherein the providerbandwidth has a characteristic impedance of 75 ohms, and the shuntresistor has a resistance value of about 75 ohms.
 9. The filter circuitof claim 1, wherein the provider bandwidth is provided by a providergroup.
 10. The filter circuit of claim 9, wherein the provider group isselected from a group consisting of a cable provider, a satelliteprovider, and a telecommunications provider.
 11. The filter circuit ofclaim 10, wherein the provider bandwidth comprises a frequency range of5 megahertz to 1002 megahertz.
 12. The filter circuit of claim 1,wherein the home network bandwidth is provided by an end user.
 13. Thefilter circuit of claim 12, wherein the home network bandwidth isselected from a group consisting of Ethernet, HomePlug, HPNA, 802.11n,and MoCA.